Joint replacement surgery seeks to replace portions of a joint with prosthetic components so as to provide long-lasting joint function and pain-free mobility for the patient.
One joint which is commonly replaced, in whole or in part, is the hip joint. The hip joint is located at the junction of the femur and the acetabulum. More particularly, and looking now at FIG. 1, the head of the femur is received in the acetabulum, with a plurality of ligaments and other soft tissue serving to hold the bones in articulating relation.
During total hip replacement surgery, and looking now at FIG. 2, the operative elements of the hip joint (i.e., the head of the femur and the acetabular cup) are replaced by prosthetic components. More particularly, during total hip replacement surgery, the head of the femur is replaced by a prosthetic ball-and-stem, and the natural acetabular cup is replaced by a prosthetic acetabular cup, whereby to provide the prosthetic total hip joint.
In a partial hip replacement surgery, only one of the operative elements of the hip joint may be replaced, e.g., the head of the femur.
The present invention will hereinafter be discussed in the context of a total hip replacement surgery, however, it should also be appreciated that the present invention may be equally applicable to a partial hip replacement surgery.
In order to replace the head of the femur with the femoral prosthesis, the head of the femur is first distracted from the acetabulum so as to expose the femoral head. Then an osteotomy is performed on the femoral neck so as to remove the neck and head of the femur from the remainder of the femur. Next, the proximal end of the intramedullary canal is prepared to receive the stem of the femoral prosthesis. More particularly, a rasp, reamer, broach, etc. is used to hollow out, clean and enlarge the intramedullary canal of the femur so as to create a cavity to receive the stem of the femoral prosthesis. Once the proximal end of the intramedullary canal has been prepared to receive the femoral prosthesis, the stem of the femoral prosthesis is inserted into the intramedullary canal so that the ball of the femoral prosthesis is appropriately presented to the acetabular cup. Typically, the ball of the femoral prosthesis is formed separately from the stem of the femoral prosthesis, and it is mounted to the stem of the femoral prosthesis at the time of use. Furthermore, it should also be appreciated that during the surgery itself, it is common to temporarily position a trial stem or broach in the femur, attach a trial ball or equivalent element to the trial stem or broach, and then temporarily reduce the joint so as to confirm the reconstruction before the actual prosthetic stem is secured in position within the femur.
In order to replace the native acetabular cup with the prosthetic acetabular cup, the native acetabulum is first prepared to receive the prosthetic acetabular cup. This generally involves reaming an appropriate seat in the acetabulum to receive the prosthetic acetabular cup. Then the prosthetic acetabular cup is installed in the seat formed in the acetabulum, and the distraction released, so that the ball of the femoral prosthesis can be seated in the prosthetic acetabular cup. In this respect it will be appreciated that the prosthetic acetabular cup typically comprises an outer cup made of metal and an inner liner made of polyethylene (or another polymer, or a ceramic, or a metal, etc.). The metal outer cup is configured so as to be received in the seat formed in the acetabulum and thereafter osseointegrate into the host bone, and the polyethylene inner liner is configured so as to be received in the metal outer cup and thereafter provide a low-friction seat for the ball of the femoral prosthesis.
During seating of the prosthetic acetabular cup in the acetabulum, it is important that the prosthetic acetabular cup be set in the acetabulum with the proper positioning, i.e., at the proper location and with the proper orientation. Such proper positioning is important in order to (i) avoid impingement between the rim of the prosthetic acetabular cup and the neck of the femoral prosthesis as the prosthetic joint is moved through a range of motions, since such impingement can result in a reduced range of motion, excessive wear, joint failure and/or substantial pain for the patient, and (ii) avoid dislocation of the ball of the femoral prosthesis from the acetabular cup as the joint is moved through a range of motions, since such dislocation can result in damage to the anatomy, joint failure and/or substantial pain for the patient.
In many cases, the surgeon seats the prosthetic acetabular cup in the acetabulum “by eye”, and thereafter confirms the proper disposition of the prosthetic acetabular cup when the distracted joint is subsequently reduced. However, this approach relies heavily on the anatomical view available to, and appreciated by, the surgeon, and errors in cup orientation (i.e., tilt) may not be discovered until after the surgery has been completed, since such errors in cup orientation can be difficult to detect interoperatively, even where X-ray imaging is available.
For this reason, various computer-guided systems have been developed to assist the surgeon in the proper placement of the prosthetic acetabular cup during total hip replacement surgery. However, such computer-guided systems frequently require that a CT scan be made of the patient in advance of the procedure so as to determine the geometry of the acetabulum. Furthermore, such computer-guided systems typically require (i) the registration and tracking of pelvic anatomical landmarks (e.g., the pubic tubercles and the anterior/superior iliac spines) prior to and during the surgery, e.g., with optical or electromagnetic trackers placed on the pelvic anatomical landmarks, and (ii) the registration and tracking of femoral anatomical landmarks prior to and during the surgery, e.g., with optical or electromagnetic trackers placed on the femoral anatomical landmarks. However, in practice, one or more of the pelvic anatomical landmarks can be difficult to physically access during the procedure. Furthermore, the optical or electromagnetic trackers must typically be applied to both the pelvic anatomical landmarks and the femoral anatomical landmarks during the surgery itself so as to track the dispositions of these body parts during the surgery. These requirements can add to the cost of the procedure, can lengthen the time required for the procedure, and can be inconvenient for the surgeon (e.g., such as where the surgeon must work around optical trackers protruding into the surgical field). In this respect it should be appreciated that optical trackers, while providing good spatial resolution, suffer from the disadvantage that they must remain directly visible at all times; electromagnetic trackers, while not requiring direct visual access, suffer from the disadvantage of poor spatial resolution.
Accordingly, there is a need for a new and improved computer-guided system for orienting a prosthetic acetabular cup in the acetabulum during total hip replacement surgery, wherein the need for a pre-operative CT scan can be eliminated, and wherein the need to physically access pelvic anatomical landmarks during the procedure can be eliminated.
In addition, there is also a need for a new and improved computer-guided system which can be used to orient prosthetic components other than a prosthetic acetabular cup, e.g., a computer-guided system which can be used to orient a femoral prosthetic component.
Furthermore, there is also a need for a new and improved computer-guided system which can be used to orient prosthetic components for joints other than the hip, e.g., a computer-guided system which can be used to orient prosthetic components in the knee.
And there is a need for a new and improved computer-guided system which can be used to determine and adjust the position of substantially any two interacting components in space.